A fluid ejection system, for example, an ink jet printer, typically includes an ink path from an ink supply to an ink nozzle assembly that includes nozzles from which ink drops are ejected. Ink is just one example of a fluid that can be ejected from a jet printer. Ink drop ejection can be controlled by pressurizing ink in the ink path with an actuator, for example, a piezoelectric deflector, a thermal bubble jet generator, or an electrostatically deflected element. A typical printhead module has a line or an array of nozzles with a corresponding array of ink paths and associated actuators, and drop ejection from each nozzle can be independently controlled. In a so-called “drop-on-demand” printhead module, each actuator is fired to selectively eject a drop at a specific location on a medium. The printhead module and the medium can be moving relative one another during a printing operation.
In one example, a printhead module can include a semiconductor printhead body and a piezoelectric actuator. The printhead body can be made of silicon etched to define pumping chambers. Nozzles can be defined by a separate substrate (i.e., a nozzle layer) that is attached to the printhead body. The piezoelectric actuator can have a layer of piezoelectric material that changes geometry, or flexes, in response to an applied voltage. Flexing of the piezoelectric layer causes a membrane to flex, where the membrane forms a wall of the pumping chamber. Flexing the membrane thereby pressurizes ink in a pumping chamber located along the ink path and ejects an ink drop from a nozzle at a nozzle velocity. The piezoelectric actuator is bonded to the membrane.